What do the B and T doors of the camera mean?

T-gate is a kind of camera shutter speed grade. Set the shutter speed knob on the T door, press the shutter button to open the shutter and start exposure. When you press the button again, the shutter will continue to open until it closes. Mostly used for shooting in dim starlight, moonlight and dim light.

Door B means that when the camera shutter button is pressed, the camera shutter opens and exposure begins; Release the camera shutter button and the camera shutter closes.

Extended data:

Under door B, the exposure time depends on how long you press the shutter, while the shutter will automatically close at a set speed. Some early cameras also had "T-gate", which is another way to control the shutter speed freely, but it is rare in today's cameras.

Different from "T-gate", "B-gate" keeps pressing the shutter button during the whole exposure process, and the exposure stops when the shutter is released, while "T-gate" starts the exposure when the shutter is pressed for the first time, and the exposure continues after the shutter is released. When the shutter is pressed for the second time, the shutter closes and the exposure stops.

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